2-6 Theory of Operation
Signal
Drive Select
Head
Load
Head
Select
Low Current
Move In
Step
Write Enable
Disc
Change
Disc Two-Sided
Index
Ready
Track
Zero
Write Protect
Read
Data
Write Data
Table 2-1. Control,
Status
and
Data
Lines
Between
the
Controller
and
Drive
Electronics
Mnemonic
DRVO-3
HEAD LOAD
HEADSEL
LOWCURR
MOVE
IN
STEP
WRITDRV
DISCHNG
TWO-SIDE
INDEX
READY
TRACKO
WRPROT
RDATA
WDATA
Function
Control
Signals
Identifies
disc
drive
with
which
controller
desires
to
communicate.
Loads the heads
and
locks the
door
on
the unit identified
by
Drive Select.
Selects
head
1 when active,
head
0 otherwise.
Reduces write current
on
inner tracks to decrease bit shift.
Causes heads
to
move toward center of disc when active
during a
Step
command.
Heads
move away from
center
when active during a
Step
command.
Causes heads
to
move in direction specified by MOVEIN.
Places
disc drive in write
mode
when active.
Status
Signals
Asserted when the selected drive is either not ready (due to
no
disc) or has a new disc inserted.
Asserted when disc
is
found to
be
two-sided.
Asserted when index hole in disc passes
photodetector.
Asserted when a disc in the selected drive has rotated for
at
least two revolutions.
Asserted when
heads
are positioned
at
track zero,
Asserted when disc in
selected
drive is write
protected.
Data
Lines
Carries read data to the controller from the drive.
Carries write
data
to the drive from the controller.
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